The invention relates to an evaporator and individual evaporator effects that are particularly advantageous for a number of processes. The invention is particularly--although not exclusively--applicable, however, to the desalination of water.
Multi-stage flash evaporators are well known, per se, for the desalinization (distillation) of water, and have been commercially used for that purpose since the 1950s. Conventional multi-stage flash evaporators use a series of interconnected effects each having horizontally extending tubes through which water to be distilled flows until it is led to a heater. From the heater the water to be distilled is passed back into the stages, countercurrent to the original direction of flow, and flashes, the vapor passing through a demistor and then into contact with the relatively cool tubes, forming condensate which is collected below the tubes. The tubes may be provided either in a cross tube configuration with a water box interconnecting the tubes and transporting the liquid within them between each stage, or they may be constructed in a long-tube configuration, where the tubes extend between each stage in a direction parallel to the flow of a liquid being flashed through the stages (counter thereto).
While conventional multi-stage flash evaporators are effective, they do not have efficiencies as great as desired.
According to the present invention, a multi-stage flash evaporator--and the individual effects therefor--are provided which can have a number of advantages compared to conventional multi-stage flash evaporator systems. According to the present invention, instead of tubes, horizontally extending, elongated dimpled plate evaporator elements are utilized. The dimpled plates are disposed in one or more sets, one stacked above the other in a tier arrangement. The dimpled plate horizontal element construction has a uniform liquor distribution, high heat transfer coefficients, and other potential advantages. The dimpled plates preferably have a construction such as shown in U.S. Pat. Nos. 3,211,219 and 3,512,239, the disclosures of which are hereby incorporated by reference herein.
According to one aspect of the present invention, an evaporator effect for a multi-stage flash evaporator is provided. The evaporator effect comprises: A horizontally elongated vessel having a top, bottom, first end, and second end. A first set of elongated in a dimension of elongation dimpled plate evaporator elements, each defining an interior passage, and having an exterior surface. Means for mounting the first set of dimpled plate evaporator elements so that they are disposed in the vessel with their dimension of elongation horizontal, and so that there are spaces between the exterior surfaces of the dimpled plate evaporator elements within the set, and so that the evaporator elements are above the bottom of the vessel, but below the top thereof. Means defining a chamber for hot liquid to be evaporated in the bottom of the vessel, below the evaporator elements. Means defining at least one channel for vapor from the hot liquid in the bottom chamber to pass upwardly into contact with the exterior surfaces of the evaporator elements. Demisting means operatively associated with the channel; and, condensate collection means disposed above the bottom chamber but below the elements, for receipt of condensate formed by vapor condensing on the dimpled plate evaporator elements, and for transporting the condensate liquid out of the vessel. The means for mounting the evaporator elements may comprise a plurality of supports--such as I-beams--which extend horizontally substantially transverse to the dimension of elongation of the plates, and mounted at the approximate mid point of the vessel (e.g. the horizontal diameter if it is circular in cross-section). The supports have openings therein through which condensate collected by the condensate collecting means can flow, the condensate collecting means at approximately the same level as the supports. Of course second, third, and even more sets of dimpled plate evaporator elements may be provided, constructed in a tier arrangement.
It is desirable to preheat the liquid to be evaporated by passing it into the interior passage of each effect, being introduced at a bottom portion into the passage of the effect elements at the second end of the vessel, and being withdrawn from the first end of the vessel at a top portion of the effect elements. The liquid to be evaporated, on the other hand, after heating thereof, passes into the bottom chamber at the first end of the vessel, and passes out of the bottom chamber at the second end of the vessel.
The dimpled plates used in the effect elements preferably are made of titanium or aluminum where the evaporator is used for the desalination (distillation) of sea water, but the plates may be stainless steel if brackish water is distilled. A sacrificial anode--such as a zinc anode--may be mounted adjacent the plates to extend their longevity.
Also according to the present invention, a multi-stage flash evaporator is provided which comprises a plurality of the effects described above interconnected with each other. A liquid heater is provided adjacent the first stage, and passes heated liquid into the bottom chamber of the first stage. The heated liquid then flows into--being flashed in each case--each of the subsequent stage bottom chambers, the pressure slightly decreasing from the first stage to the last stage. This pressure decrease may be provided by connecting the last stage to a partial vacuum, such as a steam ejector. The condensate flows from one stage to the next parallel to the evaporating liquid flow, while the liquid to be evaporated--before it is heated--flows countercurrently to these flows through the passages in the dimpled plate evaporator effects to be preheated prior to its introduction into the heater. The evaporator can either be a once-through multi-stage distillation facility, or a recycle distillation facility.
It is the primary object of the present invention to provide an effective multi-stage flash evaporator, and individual evaporator effects thereof. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.